The present invention relates to a multi-wavelength light source apparatus, particularly to a multi-wavelength light source apparatus which outputs a digital signal light with digital information superimposed thereon and in which an annular optical delay circuit is used and makes wavelength-multiplexed packets comprising digital signal lights independent of one another simultaneously output.
At present, in a field of data communication, a network mainly comprising an exchange which is xe2x80x9cexpensivexe2x80x9d but which has guaranteed high xe2x80x9creliabilityxe2x80x9d has been a mainstream.
In near future, however, a plan for not using such exchange, and shifting to a xe2x80x9clow-costxe2x80x9d next-generation data communication network utilizing an Internet apparatus has being moved forward.
In the next-generation data communication network, an Internet technique is employed to divide all information such as voice represented by telephone and dynamic image into information groups called packets to be superimposed onto a digital signal on, and the information is efficiently transmitted (by enhancing use efficiency of the circuit).
Moreover, a simple data repeater called a router constitutes a core of the next-generated data communication network.
Additionally, the existing router mainly handles an electric packet signal.
In near future, however, to increase a transmission capacity, an optical router for directly inputting/outputting an optical packet signal wavelength-division-multiplexed (WDM) is considered to be a mainstream.
Similarly as the electric router, the optical router requires a routing function of recognizing an address included in the packet and transferring the packet to a designated address.
In general, software and processor for controlling the routing function is mounted on the router.
In the optical router for handling wavelength-division-multiplexed signals, since a signal processing is complicated, it is supposedly necessary to check and confirm whether or not the software normally operates beforehand.
Therefore, in order to easily check the operation of the optical router, it is essential to employ a multi-wavelength light source apparatus which can transmit the multi-wavelength packets to be superimposed pseudo signals on.
FIG. 22 shows a constitution of a conventional representative multi-wavelength light source apparatus.
The conventional multi-wavelength light source apparatus shown in FIG. 22 includes n semiconductor laser diodes (LDs) having a single oscillation frequency 10-1, 10-2, . . . , 10-n, for example, when a wavelength multiplex number is n.
Here, each of the LD 10-1, 10-2, . . . , 10-n is able to generate each light having a frequency (e.g., an interval of 100 GHz on the basis of 193.1 THz) defined by International Telecommunication Union (ITU).
Moreover, the multi-wavelength light source apparatus includes: n LD control drivers 11-1, 11-2, . . . , 11-n for controlling oscillation states of the respective LDs 10-1, 10-2, . . . , 10-n; n optical intensity modulators 12-1, 12-2, . . . , 12-n for superimposing digital signals independent of one another on lights (wavelengths xcex1, xcex2, . . . , xcexn) outputted from the respective LDs 10-1, 10-2, . . . , 10-n and outputting the lights; n optical intensity modulator drivers 13-1, 13-2, . . . , 13-n for driving the respective optical intensity modulators 12-1, 12-2, . . . , 12-n; and an optical coupler 14 for combining and multiplexing all output lights from the respective optical intensity modulators 12-1, 12-2, . . . , 12-n.
Additionally, in the next-generation data communication network, it is expected that the transmission capacity is 1 terabit/second or more from now on. Therefore, there is high possibility that the wavelength multiplex number of the multi-wavelength light source apparatus becomes 100 or more.
Accordingly, for the conventional multi-wavelength light source apparatus, 100 or more sets of LD 10, LD control driver 11, optical intensity modulator 12, and optical intensity modulator driver 13 becomes necessary.
Therefore, in the conventional multi-wavelength light source apparatus, there are problems that the apparatus is enlarged in size and that cost becomes very high.
An object of the present invention is to provide a small-sized and inexpensive multi-wavelength light source apparatus consisting of an annular optical delay circuit which makes possible to easily keep up with an increase of a wavelength multiplex number in order to perform shipping inspection of an optical router expected to constitute a core of the next-generation network and inspection during construction of the network.
To achieve the aforementioned object, according to a first aspect of the present invention, there is provided a multi-wavelength light source apparatus comprising:
a tunable light source (1) for successively changing and outputting a plurality of output lights different in wavelength from one another;
an optical intensity modulator (2) for outputting a modulated signal lights obtained by modulating an amplitude of the output light outputted from the tunable light source over a predetermined time;
an optical coupler (3), optically connected to the optical intensity modulator, for receiving the output light from the optical intensity modulator;
an annular optical delay circuit (4), optically connected to the optical coupler, for delaying a part of the output light from the optical intensity modulator over a time longer than the predetermined time; and
an optical gate device (5), optically connected to the optical coupler, for receiving the output light from the optical intensity modulator and the light passed via the annular optical delay circuit to open a gate at a timing and a time width such that all of the signal lights modulated over the predetermined time are included one by one for each of the plurality of wavelengths.
Moreover, according to a second aspect of the present invention, there is provided the multi-wavelength light source apparatus of the first aspect, comprising an optical amplifier (6), optically connected into the annular optical delay circuit (4), for amplifying a light intensity of the light inputted to the annular optical delay circuit.
Furthermore, according to a third aspect of the present invention, there is provided the multi-wavelength light source apparatus of the second aspect, comprising an optical frequency filter (7), optically connected into the annular optical delay circuit (4), for passing only the plurality of lights different in wavelength from one another outputted by the tunable light source.
Additionally, according to a fourth aspect of the present invention, there is provided the multi-wavelength light source apparatus of the first aspect, comprising an optical digital device (8), optically connected into the annular optical delay circuit (4) and provided with characteristics such that light transmittance is high when the intensity of the light inputted to the annular optical delay circuit exceeds a predetermined threshold value, and the light transmittance is low when the light intensity indicates the threshold value or less.
Moreover, according to a fifth aspect of the present invention, there is provided the multi-wavelength light source apparatus of the second aspect wherein the optical amplifier (6) is an optical bistable device for selectively amplifying only the plurality of lights different in wavelength from one another outputted by the tunable light source and amplifying an alternating-current component of the modulated signal light at an amplification factor higher than that of a direct-current component.
Furthermore, according to a sixth aspect of the present invention, there is provided the multi-wavelength light source apparatus of the first aspect, comprising: an optical amplifier (6), optically connected into the annular optical delay circuit (4), for amplifying a light intensity of the light inputted to the annular optical delay circuit; and an optical digital device (8), optically connected into the annular optical delay circuit (4) and provided with characteristics such that light transmittance is high when the intensity of the light inputted to the annular optical delay circuit exceeds a predetermined threshold value, and the light transmittance is low when the light intensity indicates the threshold value or less.
Additionally, according to a seventh aspect of the present invention, there is provided the multi-wavelength light source apparatus of the third aspect wherein the optical frequency filter (7) is an asymmetric Mach-Zehnder interferometer.
Moreover, according to an eighth aspect of the present invention, there is provided the multi-wavelength light source apparatus of the third aspect wherein the optical frequency filter (7) is a Fabry-Perot resonator.
Furthermore, according to a ninth aspect of the present invention, there is provided the multi-wavelength light source apparatus of the first aspect, comprising:
a tunable light source driver (101) for driving the tunable light source (1) in a predetermined state;
an optical intensity modulator driver (201) for driving the optical intensity modulator (2) in the predetermined state; and
an optical gate device driver (501) for driving the optical gate device (5) in the predetermined state.
Additionally, according to a tenth aspect of the present invention, there is provided the multi-wavelength light source apparatus of the ninth aspect, comprising a controller (100) for controlling the tunable light source driver (101), the optical intensity modulator driver (201), and the optical gate device driver (501) in the respective predetermined states.
Moreover, according to an eleventh aspect of the present invention, there is provided the multi-wavelength light source apparatus of the third aspect, comprising an optical digital device (8), optically connected into the annular optical delay circuit (4) and provided with characteristics such that light transmittance is high when the intensity of the light inputted to the annular optical delay circuit exceeds a predetermined threshold value, and the light transmittance is low when the light intensity indicates the threshold value or less.